Pneumatic spring



March 6, 1934. R. SEFTON 1,950,013

PNEUMATIC SPRING Filed Nov. 28, 1931 2 Sheets-Sheet 1 -Rz ckarcz(537F607? March 6, 1934. R. SEFTON PNEUMATIC SPRING Filed Nov. 28, 19312 Sheets-Sheet 2 ITZUIzZor k Richs/rd Sejlom Patented Mar. 6, 1934UNITED STATES; PATENT. OFFICE e,

PNEUMATIC SPRING Richard Sefton, Cleveland, Ohio Application Novemberzs, 1931,s'eris1 No. 577,765

14 Claims. (Cl. 267-65),

My invention relates to pneumatic springs, and

-it relates more particularly to a device which is adapted to be used inlieu of the shackles which are now commonly employed between the end ofthe spring and the supporting bracket of the chassis frame of anautomobile, to act as an auxiliary spring, or shock resister.

The principal object of my invention is to provide an auxiliarypneumatic spring for motor vehicles and the like, which is simple andefiicient, which is relatively inexpensive, and which is so constructedand arranged that leakage. of the air isreduced to a minimum, to the endthat the requisite air pressure will be. properly maintained.

A further object of my invention is to provide a construction andarrangement whereby the device may be easily dismantled for the purposeof examination andrepair when required, and readily adjusted, withoutdismantling, for the purpose of increasing the pressure on the sealing.or packing members, in the event of leakage.

The nature and characteristic features of myinvention will bemorereadily understood from the following description, taken inconnection with the accompanying drawings forming part hereof, in which:H 1,

Figure 1 is a vertical, central, sectional view of a pneumatic springembodying the main fea tures of my present invention;

Fig. 2 is a horizontal section thereof, taken approximately on the line22 of Fig.1;

Fig. 3 is a horizontalsection taken approximately on the line 3-3 ofFig. 1; I

Fig. i is a horizontal, section takenmately on the line4-4 of Fig. 1;Fig. 5 is a horizontal section mately on the line 55 of Fig. 1';

Fig. 6 is an enlarged central section ofamember, detached, used forproviding a high pressure air chamber for the purpose of increasing theefficiency of the engagement of a cup leather,

employed at the upper'endof the piston;

Fig. 7 is an enlarged perspective view of a bolt l member, detached,used for limiting the extent of the movement of the piston with respectto the cylinder, and for preventing improper separation thereof; t iFig. 8 is a perspective view of a gland member, detached, used inconnection with the member shown in Fig. 6; and

Fig. 9 is a side elevation, on a reduced scale, of the pneumatic spring,illustrating a preferred manner of connecting the same to the vehicleparts.

vehicle, in connection withwhichthe device is approxitaken approxiItwill, of course, be understood that the drawings and descriptionherein contained areillustrative merely, and that various modificationsand changes may be made in the structure disclosed without departingfromthe spirit ofthe invention. I

Referring to thedrawings, in the particular embodiment of my invention.therein shown,,10 is a cylinder, in which a hollow piston 11 is slidablymounted. The'cylinder 10 is pivotally connected'by means of trunnions 12to brackets 13, which are secured in any suitable mannensuch for exampleas by means of bolts 14, to a portion of the chassis frame 15 of theautomobile, or other used. The. lower end of the piston 11 ispivotallyconnected,.-by means of a bolt 16, to an eye 17 carried at theend oftheupper member 18 of the leaf spring which is usually secured tothe axleof the vehicle. .The upper end of the cylinder 10 extends upwardly, toprovide an internal air chamberj19. i

The piston 11 is made hollow to provide an auxiliary chamber 20, whichis in communication with the air chamber19 provided in the top of thecylinder 10', by means of a tube 21', which is mounted-in thev top ofthe piston 11 and extends upwardly therefrom. Thetwo air chambers thusprovided in the top of the cylinder 10 and in the piston 11 are,together, of sufiicient capacity to secure the requisiteresiliency inthe operation of the device. v I

Inasmuch as. the weights or the vehicles to be supported varyconsiderably, a quantity of oil .22 may be placed in the chamber 20 ofthe piston surfaceofthewall of the cylinderlO. The cup leather 23 isheld in position on the top of the piston 11, by means of a disk 25,which is threaded on a continuation of" the threads by means of whichthetube 21 is mounted in" the upper end of the piston 11.

A high pressure air chamber 26 is provided by a member, 27, comprising apair of concentric sleeves 28 and 29, ahorizontal wall30. Thelower endof the outer sleeve 28 of the member 27 is provided with a lip 31, theouter surface of which engages the wall of the cylinder 10. i i V piston11 is a 96 united at the topby means' of t 3 member. 2'? is alsoinclined; .to provide a-seatfor ridges being provided so that; whenpressure is imparted to the member 27', in the manner to be hereinafterset forth; said pressure will be exerted mainly in a downward directionupon the lip portion 24.0: the cup leather 23.

The upper face of the lip portion 31 of the out:

er sleeve 28' of the member 27 is also inclined," to serve as a seat fora sealing or packing ringv33; I:

made of a suitable packing material. A metal,

sleeve 34 is seated in the annular. space betweenf vthe outer surface ofthe, outer sleeve 28;;of-;the

member27, and the inner working faceof the cylinder flO. #Thelower endofthe sleeve Ba lsinclined andbears against the packing The pressure inthe air chamber 19 isfmpartedi" by m'eansof thesleeve Bet-totheupackintring 331:; An. annular plate ,35: is mounted uponr the upperhorizontal .wall 30 of a the member 27, and

serves to retain the sleeve 34 in position.

extending lip portion 36, the inner face-ofuwhich engages theoutersurtace 'oflthe tube 21 which is moimtfed inthetdpaofthepiston1l.-, The upper surface of the lip portion 36 0f the sleeve 29of the a sealing-or pa'cking ring 3'7, made of suitable packingmaterial-,whichserves to, prevent leaki at the upper end age between thehighmressure chamber 26 and the airchamber l9iin'the top-ofthe'cylinderlfl;

Mounted in the annular space between the out er surface or the tube 21and the innerrsurface of the sleeve portion'29 of the member 2'7, ista'ring 38j-ha'ving an inclined lower face which;

bears against the packing ring 37; A gland 39 is threaded on the upperend of the tube 21, and a heavy coil; spring 'im'surrounding the tubeZl,

is interposed between the ring 38 and the gland 39, for the purpose ofcompressing thepacking ring 37, and simultanously imparting pressure'tothelip portion24 of the cup leather 23, by means of he lip '31 carriedatthe lower end of the outer lsleeve28 of the member 27-. l

of the spring 40 is made by advancing or re tra'cting the gland 39 uponthe threads provided 0f the tube Z L -ihE'inahIiBl to be presentlydescribed. Extending upwardly from the *top horizontal wall 30 ofthemember 2'? is a tubular stem al having mountedtherein a. check valve i2of a type connnonly-employed" t in the'air valves of automobile tires,except that the packing thereof'is made or a material which will not beaffected by the oil used in the device. I Such valves are nowwellknownjand readily prot curable so that the same need not be furtherde- For the purpose or l mit n fxteat, for the movementbetween thepiston 11 and the cylinder lOQwhereby the packing member might becomedisarranged,j;as well as ttorithe purpose of preventing separationcofthe piston from the'cylinder, there isprovided a limiting devicecomprisa bolt 43, having an enlarged threaded head portion 14, which isymounted in a suitableinternalboss 459.1: the upper end of thecylinder'10 The mainshank of the bolt 43 has flattened sides, andthe lowerfendportion ificofsaid bolt by ,v v a a 1,950,01 The lower face of the lipportion 31"ofthe outer sleeve 28 of the member 27 is inclined, andprovided with a series of annular ridges'32, which engage the upper,complementally inclined face} of the lip'portion 24 of the cup leather23, the

bolt; but larger, in dimfiwonsttopermit the air vthe inner surface of the cylinder 10 and theparts inserted" through cated through said oiltothe lip portion 24 of the lat vehicle.

, usual r the cylinder -10, and piston ll, respectively, and

has similarly flattened sideaxwhich, however,

main shank of the bolt. ,A small portion ofthe bolt 43, adjacent thelower end 46, is made cylindrical, but reduced in diameter, as at 47,cor- "responding to the distance between the flattened sides of the mainshank of the bolt and those of j I the lower end portion thereof;

In the normal assembly of the device, the main shank of the bolt 43extends through an opening re m the gland a9; 'this opning being shapedsimilarly to the cross section of the ofthe bolt,but largerindimensions, whereby the 1 main shank bolt will be looselyfitting withrespect thereto :(see Figs. land 2) ,:so as to permit the air to passbetween the chambers '19 and 20, provided, re-

spectively, in; the upper end of the cylinder 10 andthe interior'oithepisto'n 11, the tube 21, as'

* hereinbe'for; setforth, serving'a's a means of 7 communication?between these chambers.-

The main shanl; ofthe bolt 43 also extends through an opening fi5provided in thehead of larlytto theicross section of the main shank ofthe topasstherethrough. H a

'For the purpose of prcviding the requisitepres- .sure within the airchambers 19 and 20,there isprovided an inlet check valve.4,9.t iwhich isalso of t a" construction similar to that of the type of. valve commonlyused for, inflating automobile tires, the barrel of: valve; Ail beingmounted in the. wall: at the upper end 'of the. cylinder 10, and having)its outer. and provided with a threaded nipple 50,mwhereby the hose ofanair pum'pmay be connected thereto. r

' A a quantity for oil 51 is placed in the device, in the spaceimmediatelyabovelthe top of the'memberd'tpthus insuring" properlubrication between which slidably engage the same, and also between theouter surface-o1'fthetube21 and the parts which slidably engage thesame. "This oil may be v x an opening 52 provided in the upper portionofthefcylinder 10, which is'nor mall'y closedeby l means of a threadedplug 53.

A' duantity oftoil 54 is also placed in thebot tom of the air chamber26, provided by means of t the member 27; so that the pressure of theairAdjustment of the pressure imparted by means contained withinthef'chamber 26 is communi 'cupleather23.

chanibers19 and; 20, provided, respectively, in f the upper end of thecylinder 10 and thein-V terior of the piston .ll the pressure" dependingin each instanqefuponthe' weight of theparticu- ,It will, j of: c urse,be understood" that the air within the chamber 26; provided -by themember J *27 andjthe parts associated therewith, will initially beofthesamepressurefas theairf in the. chamber 19;.at the upper end of thecylinder 10.

the .vehicle is's'ubjected to the Oadshocks, theairlis compressed tovary Wh'en however,

ing degrees within the chambers 19 and;2(),in-

whenever the pressure within "the chamber 19 ex- 3 ceeds that in thechamber 26, acertain quantity of this air of higherpressure will beforced into 'the chamber 26 are'at rlg htan gles to the flattened. sidesof the It will therefore be apparent that thepres'sure of the air in thechamber 26 will ordinarily be in excess of that of the air in the,chambers 19 and 20." This pressure will be exerted against the lipportion 24of'the cup leather 23, therebyincreasing the efiiciency of itsengagement with the inner working surface of the, cylinder 10.

It will be noted, however, that any increasein pressure within thechamber 26- will act against the tension of the spring 40, and thusrelieve the downward pressure of the'lip portion 31 of the member 27:against the upper surface of the lip portion '24 of the cup leather.'23. and vice versa; Consequently, the seal. provided by thelip portion24 of the cup leather 23 will be maintained at all times substantiallyuniform, notwithstanding variations of pressure within the chamber 19,-provided at .the upper end ofthe. cylinder 10. t

It has been found in practice that, with the foregoing arrangement, therequisite freedomiof movement between the piston 11 and the cylinvder 10may be obtained with a minimum of leakage past the cup leather.

air to occur, by reason of the oil 'seals'provided bymeans of the oil 51which is placed immediately above the member 27, and the oil 54' whichis placed in the lower portion of the chamber 26.

It will :also be found that leakage of theoil will be exceedingly smallin amount, audit will not be necessary to replenish the supply ofthesame very frequently. In fact, no more oil will leak past thanisnecessary for the normal lubrication oftheparts. In theevent that itshould be found necessary to adjust the pressureexerted'by the lipportion -31 of the member 2'7 against the upper surface of the lipportion 24 of the cup leather 23, it will be necessary merely to removethe bolt 16 by means of which the lower end of the piston ll isconnected to the spring of the vehicle, after which the piston isextended with respect to the cylinder until the'lowerend portion 516 ofthe bolt 43 engages the upper wall of the piston adjacent the opening55,: whereupon, by turning the piston. 11 a half revolution at a time;about its vertical axis, the gland 39 will be rotated upon its threadsto change the tension of the spring 40, this action being-accomplishedby'reason of the engagement of the flattened sides of the of thecushioning air past the piston is eliminated; and this without exertingundue pressure upon" the sealing elements, which would in terfere withthe requisite freedom of movement between the piston and the cylinder.

I claim:

' 1. In apparatus of the character described, a cylinder; a pistonslidaoly mounted therein; a cup leather secured to the top of thepiston; said cup leather having a lip'portion extending upwardly andbearing against the inner surface of cylinder; the upper portion of thecylinder for: ing an air chamber adapted to contain a volume of airunder pressure; a hollow member by the'pistc-n above the cup leather inwhich is contained a quantity of air under pre'ssurenor- It will beobserved that it will be impossiblev for a direct leakage ofchamber-a'tthe top of the cylinder, thepressure mally higher than thepressure of the air in the" of the airin said'member being exertedagainst the lip portion of the'cup leather; a portion of said hollowmember having a port forming a communication betweehthe'interiorof saidholl'ow member and the air chamber at the top of thecylinder; and acheck valve mounted insaid port; said hollow member having a portion beaing downwardly on the top. of the lip portion of the'cup leather. r

2. In apparatus of the character described, a cylinder; a pistonslidably mounted therein; a cup leather secured to the top of thepiston, said "cup leather having a'lip portion extending up wardly andbearing against theinner surface of the cylinder; the upper portion ofthe cylinder forming an-air chamber adaptedto contain" a volume of airunder pressure; hollow member carriedby'the piston'above the cupleatherin which is contained a quantity of air under pressure normallyhigher than the pressure of the air in the chamber at the top of thecylinder, the pressure of the air in said ineinb'er being exertedagainst the lip portion of the cup leather; a portion of said hollowmember liaving a'port forming acommunieation between the interior ofsaid hollow member and, the air chamber' at the top ofthe cylinder; acheck valveniounted I in said port; said hollow member having apes tionbearing downwardly on the top of the lip portion of the cup leather; acoil spring adapted to a downward pressure upon the hollow member; andmeans for adjusting thetension of coil spring. I

'8. In apparatus of the character described, a

cylinder; apiston slidably mounted therein; a

cup leather secured to the top of the piston, said cup leather'having alip portion extending upwardly and bearing against the inner surface ofthe cylinder; the upper portion of the cylinder forming an air chamberadapted to contain a volume of air under pressure ;a hollow-membercarried .bythepiston above the cup leather in which is contained aquantity of air under pres sure normally higher than the pressure of theair in the chamber at the top of the cylindenthe.

pressure of the airin said member being exerted against the lip portionof the cup leather; a portion of said hollow member having a portforming a communication between the interior of said hollowmeinber andthe airchamber at the topof thecylinder; a check valve mountedin'saidport; said-hollow member having a portion hearing downwardly on the topof the lip portion of the cupleather; a tube secured to the top of thepiston and extending upwardly therefrom through the aforesaidhollo-wmember; a coil spring surrounding saidtube and adapted to imparta downward pressure upon the hollow memberfand means for adjusting thetensionof the coil spring by rotating the piston with respect totheeylinden 4. In apparatus of the -character,described, a,

cylinder; a piston slidably mounted therein; cup leather secured to thetep'of the piston, said cup leather having a lipportion extendingupwardly and bearing against the inner surface of the cylinder; theupper portion of the cylinder forming an air chamber adapted'to containvolume of air under pressure; a-hollow member carried by the pistonabovethe cup leather in res which is contained a quantity of air under"surenonnally higher, than the pressure of the l air in'thechamber'at'the top of thecylinder, the

against the lip portion of the cuprleather; a por- 1 tion of said hollowmember'having a portfforming port; ,said hollow member having a portionbearing downwardly on the top'of the lip DOI'ti QIl Of i the cupleather; packing interposedbetween said F vi il-hollow member and theinner surface of the" a communication-between the interior of said,"hollow member and theair chamber at the top of the cylinder; a checkvalve mounted in said cylinder; a sleeve mounted abovelsaid packinghaving iitsylower surface bearingT against said Qpacking: and itsiuppersurface exposed to; the

pressure of the air contained within the chamber at the top ofthecylinderj atube securedtoathe top of;the piston'and extendingupwardlytherefrom throughrthe aforesaidvhollow member; a

1 coil spring surrounding said tube and adapted to'impart a downwardpressure uponthe hollow member; packing surrounding "said tube andinterposedfbetweenthe lower end of the spring and a portion of-the-hollow member and means for adjustingtheftension of'jthe coilspringby roj- ,airchamber exceeds'thatfinthehollowmember;

the, piston beinghollow, and 'a tube secured there to, forming ercommunication between i the air 1 tating thepistonwith respect to thecylindenj a 5. In' appara'tu's of the character, described a cylinder; apiston slidablymounted thereinja 30. forming an air chamber adapted tocontainer volume of air'underpressurepa hollow member cup leathersecured'to the top -ofthe piston, said 7 cup leather having a lipportion extending .up-

ward ly and bearingagainstthe-inner surface of, the cylinder; the upperportion of. the cylinder,

carried by the pistonabove the cup leather'in which is'containedaquantity of air under pressure normally higher than the pressure of theair in the chamber at the top "oft-the cylinder, the pressure ofthe airin said member beingexerted against the lip portion of the cup leather aportion of said hollow member havinga port formmg a communicationbetween the interior of said hollow member-andthe air chamber at the topof the. cylinder; acheck valve mounted inrsaidf portf'said; hollowmember havinga portion bearting downwardlyon thetop of the lip portionof the cup, leather; packing interposed between, said hollow member andthe innersurface of the cylinder; a sleeve mountedabove-saidpackinghaving'its lower surface bearingagainstsaid pack- 'ingand its upper surface exposed to the pressure of the air containedWithin the chamberat the top of the cylinder; a tube secured to ,thetopot {the piston and extending upwardly therefrom through the aforesaidhollow member; a gland, gthreaded' on the upper {endof saiditubej a coil1'55 spring surrounding said tube and adapted to impart adownward'pressure upon the hollow member; packing, surrounding said'tubeandinter posed between the'lower end offthe spring and a portion ofthQhOllOWIl'lBl'Ilbfilfi and a limiting device comprising a boltextending downwardly from the upper end of the cylinder, the main vshankportion-of said bolt beinglof non-circular cross section and extendingthrough a, similarly shaped opening in the gland which is threaded onthe top of the tube, whereby the-tension of the coil spring may beadjusted by rotating the piston with respect to the cylinder.

6. In apparatus'of the character described, a

: cylinder; La pistongslidably mounted, therein; a

packing device carried by thetop of the piston .7 r and bearing againstthe inner surface of thecyl-g inder; the upper portion of thecylinder'forming;

an airbhamber adapted to contain a volume of air under pressure; ahollow member carried by the piston above the; packing device in-iwhichH v I "1f;950',013 M pressure of the air in said member beingexertedacon'tained a quantity ot air under pressure nor mallyfhigher than the'pressure of the air in the chamber. at theatop of the cy1inder,;.th epressure of the air in said amerhber beingtexerted against thepackingxdeviceirthe piston being hollow, and j -a tube securedtheretotorming-acommunication between the:airjchamber'providedatlthetoproi the cylinder andatherinterior offthepi'ston:

cylinder; as piston. slidably; mounted therein a packing device {carriedby 1 the top of the piston and bearing against the inner surface of'thet cylinder; the upper portion of" the cylinder form'- ing anair chamberadaptedito containa volume Zof airunder pressure; jatholl'ow membercarried by the pistenabove'the packing device inwhi'ch is contained aquantity ofair under pressure nor-- mally higher than thejpressurejoithe airin the chamberat the topofthecylinder, thepressure of the airinsaid rnember'beirig exertedagainst- ,the packing device, andmeansfor-'tr'apping'air" in said hollow member from the air chamber inthe top ofithecylinderwhenthepressure in said l chamberprovided at thetop the interiorof the piston:-

wardly and bearing againstthe inner surface of volumelofj airunderpressure; a hollow member 7. Injapparatus of the character ;described,-a

of the cylinder and the:cylinder;Ythe upper portionoft'hef cylinder" lforming an air chamber adapted to contain a o i carried by the pistonabove the cupdeatherlin -i which is contained a quantity of airlllldgiljJlCS surenormally higher than the pressure of the air inrth'e;chamber at the top of the cylinder,

the pressure of the airln saidrnembenbeing exerted againstthe lipportionof the cup leather; the piston being hollow, and'a tube securedthere- 7 ;to forming a communication between the air 1 chamber provided"at the top of'the cylinder and 9. In apparatus of the characterdescribed, a p

the interior of the pistons;

cylinder ;1 1 a; piston" slidably mounted therein; a

cup leather secured to the top *of the piston, said, cup leather havinga lip portion extending upwardly and bearingi= against thefiinnersurface oi the cylinder; the upper" portion of the cylinder forming anair,chamber*adapted to contain a volume'oi air under pressure; a; hollowmember carried yH-the piston abovethecup leather in ,WhiChlS containedaquantity of airunderpres air in thechambenatnthe top of the cylinder,the'pressure of {the air in .;said member being exerted against thelipportion oi the cup leather;

130, sure ridrmally hi her an thepressure of the i a portionofsaid-hollow member having a port 'forming a communication; between-theinterior of said hollow; .mernber :andjthe: air chamber at the top ofthecylinder; avcheck valve mounted in said port; thepiston beinghollow,and a tube secured thereto forming a communication; bea "tween, the airchamber provided at the top of .the cylinderandthe interior'of thepiston. j

lo li rapparatus of the character described, acylinder, a pistonslidalbly mounted therein; a'

cup leathersecured to the top of the piston, said cup leather havingalip portion extending upwardly and bearing against the inner'sur'fa'c'eof ".thecylinder; the, upper portion "of the cylinder forming an airchamber adapted tocontaina volume of .air under pressure; a hollowmember carried by the piston, abovethe. ;cupleather in which iscontained a quantity ofair underprese.

of said hollow member and the ,air chamber at the top of the cylinder; acheck valve mounted in said port; said hollow member having aportion'bearing downwardly on the top of the. lip

portion of the cup leather; the pistcnbeing hollow, and a tube securedthereto forming a com- -,munication between theair chamber provided atthe top of the cylinder and the interior of the piston.

11. In apparatus of the character described, a cylinder; a pistonslidably mounted therein; a cup leather secured to the top of thepiston, said cup leather having a lip portion extending upwardly andbearing against the inner surface of the cylinder; the upper portion ofthe cylinder forming an air chamber adapted; to contain a volume of airunder pressure; a hollow member carried by the piston above the cupleather inv which is contained a quantity of air under pressure normallyhigher than the pressure of "the air in the chamber at the top of thecylinder, the pressure of the air in said member being'exerted againstthe lip portion of the cup leather; a portion of saidhollow memberhaving'a port forming a communication between the interior of saidhollow member and the'air chamber at the top of the cylinder; a checkvalve'mounted in said port; said hollow member having a portion bearingdownwardly on the top of the lipportion of the cup leather; a coilspring adapted to impart a downward pressure upon the hollow member;means for adjusting the tension of said coil spring; the piston beinghollow, and a tube secured thereto forming a communication between theair chamber provided at the top of the cylinder and the interior of thepiston,

12. In apparatus of thecharacter described, 'a cylinder; a pistonslidably mounted therein, a .cup leather secured to the top of thepiston, said cup leather having a lip portion extending upwardly andbearing against the inner surface of the cylinder; the upper portion ofthe cylinder forming an air chamber adapted to contain a volume of airunder pressure; a hollow member carried by the piston above the cupleather in which is contained a quantity of airunder pressure normallyhigher than the pressure of the air in the chamber at the top of thecylinder; the pressure of the air in said member being exerted againstthe lip portion of the cup leather; a

portion of said hollow member having a port forming a. communicationbetween the interior of said hollow member and the air chamber at thetop of the cylinder; a check valve mounted in said port; said hollowmember having a portion bearing downwardly on-the top of the lip portionof the cup leather; a tube secured to the top of the piston andextending upwardly therefrom through the aforesaid hollow member; a coilspring surrounding said tube and adapted to impart a downward pressureupon the hollow member; and means for adjusting'the tension of the coilspring by rotating the piston with respect to the cylinder; the pistonbeing hollow, and the tube secured thereto forming a communifcationbetween the air chamber provided at the the hollow. member; tube andinterposed top of the cylinder and interiorof the piston.-

13.V-In apparatus of the character described; a cylinder; a pistonslidably mounted therein; a

' cup leather secured to the llOPfOf the piston, said cup leather havinga lip;v portion; extendingupwardly and bearing' against the innersurface of thet d th upp r p rti of the rvfin r forming an air chamber;adapted to contain a volume of air under pressure; hollowinember carriedby the. piston above the cup leather in which is contained-a quantity ofair under pres-' sure normally higher than the pressure of the air inthe chamber at the top of the cylinder, thepressure oi the airinsaidmember being exerted against the lip portion of the cup leather; aportion of said hollow member having a port forming a communicationbetween the interior of said hollow member and the air chamber at thetop of the cylinder;-a check valve mounted in said port; said hollowmember havinga portion bearing downwardly on the topof the lip portionor" the cup leather; packing interposed between said hollow member andthe inner surface of the cylinder; a sleevemounted above said packinghaving its lower surface bearing against" 1 said packing and its uppersurface. exposed to the pressure v of the air contained within thechamber at the top or" the cylinder; a tube secured to the top of thepiston and extending upwardly therefrom through the aforesaid hollowmember; a coil spring surrounding said tube and adapted to impart adownward pressure upon packing surrounding said between the lower end ofthe spring and a portion of the hollow member; 1 and means for adjustingthe tensionof the coil spring by rotating the piston with respect to thecylinder; the piston being hollow, and the tube secured thereto forminga communicationbetween the air chamber provided at the top of 1 thecylinder and the interior of the piston.

14. In apparatus ofthe character described, a c cylinder; a pistonslidably mounted therein; a cup leather secured to the top of thepiston, said cup leather having a lip portion 'extending'up 1 wardly andbearing against the inner surface of the cylinder; the upper portion ofthe cylinder 3 iorming an air-chamber adapted to contain a. volume ofair under pressure; a hollow member carried by the piston above the cupleather in which is-contained a quantity of air under pressure normallyhigher than the pressure of the air in the chamber at the top'of thecylinder, the pressure of the air in said member being exerted againstthe lip portion of the cup leather; a porlow member and the innersurface of the cylinder;

a sleeve mounted above said packing having its lower surface bearingagainst said packing and its .upper surface exposed to the pressure ofthe air contained within the chamber at the top of the cylinder; a tubesecured to the topof the piston and extending upwardly therefrom throughthe aforesaid hollow member; a gland threaded on the upper end of saidtube; a coil spring surrounding said tube and adapted to-impart adownward pressure upon the hollow member packing surrounding said tubeand interposed between the lower end of the spring and a portion of thehollow 1 ame compasmggwu extndipg downwardly from the upper end of theing"otnon"-circu1a cfoss section anditending through a similarly openingin the gland which is threaded onthe 0f the tube, where:

cylinder, the ma n Ishankpdrtibn of Said-bolt be-L chamber provided" ittheiqp dt the cylinder and theintxfipr pf thefpistpn A '1 I v y byrotating th istmmp-rs emo the cyiind fiu the piston being hollow.-and-the-tubeflseuredl thereto forming si communication between the air

